1. Field of the Invention
The invention is directed to an improved fuel injection apparatus for an internal combustion engine.
2. Description of the Prior Art
A fuel injection apparatus known from EP 0 987 431 A2 has a high-pressure fuel pump and a fuel injection valve connected to it for each cylinder of the internal combustion engine. The high-pressure fuel pump has a pump piston that delimits a pump working chamber and is driven into a stroke motion by the engine. The fuel injection valve has a pressure chamber connected to the pump working chamber and an injection valve element that controls at least one injection opening; the pressure prevailing in the pressure chamber can move the injection valve element in the opening direction counter to a closing force in order to open the at least one injection opening. A control valve controls a connection of the pump working chamber to a relief chamber and a pressure source. When the control valve is open, the pump working chamber is filled with fuel from the pressure source during the intake stroke of the pump piston. The object is for the high-pressure pump to produce a high pressure even at a low speed of the engine, thus achieving a high performance and a high torque of the engine. The pressure produced by the high-pressure pump, however, increases with the speed of the engine; the maximal pressure achieved must be limited in order to assure a sufficient service life of the high-pressure pump. With a given drive unit of the high-pressure pump and a given diameter of the pump piston, a design compromise must be struck in order on the one hand to achieve a sufficiently high pressure at a low speed and on the other hand, not to exceed the maximal pressure that has been predetermined for reasons related to the service life.